In the beginning of 1990s, the transport network evolved from a Plesiochronous Digital Hierarchy (PDH) network to a Synchronous Digital Hierarchy (SDH) network, providing a synchronous transport platform with large capacity for voice services and data services. With the rapid development of the bandwidth for data services, the bandwidth and dispatching capability of the single wavelength SHD network no longer satisfy the growing demand. A Dense Wavelength Division Multiplexing (DWDM) network can well address the issue of lack of bandwidth. The DWDM network, when converged with an Optical Transport Network (OTN) technology, can provide an administrative monitoring OTN network with a great network survivability and a powerful dispatching capability on the basis of wavelength and sub-wavelength level. With such OTN network, wavelength and sub-wavelength service can be provided rapidly.
The dispatching capability of OTN network primarily includes Optical Channel (OCh) dispatching capability based on wavelength level and Optical channel Data Unit-k (ODUk) dispatching capability based on sub-wavelength level.
The OCh dispatching technology on wavelength level, widely adopted by the industry, includes a Reconfigurable Optical Add-Drop Multiplexer (ROADM), Wavelength Selective Switch (WSS), etc., offering flexible wavelength selection and Add-Drop multiplexing functions.
ODUk dispatching based on sub-wavelength level supports 3 types of rate granularities: ODU1 of 2.5 Gbps, ODU2 of 10 Gbps and ODU3 of 40 Gbps. An asynchronous space division dispatching chip can be used to implement the space division dispatching with the above granularities. A relatively mature one used in the industry is the asynchronous space division cross connect chip at a granularity of 2.5 Gbps.
The structure of an ODUk (k=1, 2, 3) frame is similar to that of an OTUk. FIG. 1 illustrates a format of OTUk (k=1, 2, 3) frame. As shown in FIG. 1, OTUk frame has a block structure with a size of 4 rows×4080 bytes/row including a 4×16 overhead portion, a 4×3808 payload portion and a 4×256 forward error control (FEC) portion. The 4×16 overhead portion primarily includes an OTUk frame alignment (FA) data situated in row 1, bytes 1˜6, OTUk overhead (OH) data situated in row 1, bytes 7˜14, ODUk overhead (OH) data situated in row 2˜4, bytes 1˜16, and OPUk OH data situated in rows 1˜4, bytes 15˜16, where k=1, 2, 3.
ODUk (k=1, 2, 3) frame plus FEC portion forms the OTUk frame. The size of the ODUk frame is 4 rows×3824 bytes/row=15296 bytes.
Considering that the current asynchronous space division dispatching is at a granularity of 2.5 Gbps, OTU1/ODU1 signal does not have the issue of splitting and combination. The existing asynchronous space division dispatching is to split OTUk/ODUk (k=2, 3) signal into a plurality of units each having 16 bytes, thus forming a plurality of signals at 2.5 Gbps level. For instance, OTU2/ODU2 signal of 10 Gbps needs to be split into 4-bit parallel signals. OTU3/ODU3 signal of 40 Gbps needs to be split into 16-bit parallel signals.
When splitting, the following should be considered. In order to recover the original signal from the split signals, sink frame alignment needs to be performed on each split signal, which means that the FA data, i.e., bytes 1˜6 in row 1 of each frame, are assigned in average to a signal of 2.5 Gbps in each channel.
FIG. 2 is a schematic of existing process for splitting OTU2 signals. Referring to FIG. 2, the splitting process is as follows.
At the transmitting side, the splitting process is as follows.
1. The process for splitting OTU2 signals received during the 4n+1th (n=0, 1, 2 . . . ) frame period is described below.
Bytes 1˜16 in each row are assigned to a first signal channel of 2.5 Gbps, i.e., a first channel. Bytes 17˜32 in each row are assigned to a second channel. Bytes 33˜48 in each row are assigned to a third channel. Bytes 49˜64 in each row are assigned to a fourth channel. Bytes 65˜80 in each row are assigned to the first channel. Bytes 81˜96 in each row are assigned to the second channel . . . . The rest may be deduced by analogy until all the data in each row included in the frame are assigned.
2. The process for splitting OTU2 signals received during the 4n+2th (n=0, 1, 2 . . . ) frame period is described below.
Bytes 1˜16 in each row are assigned to the second channel. Bytes 17˜32 in each row are assigned to the third channel. Bytes 33˜48 in each row are assigned to the forth channel. Bytes 49˜64 in each row are assigned to the first channel. Bytes 65˜80 in each row are assigned to the first channel. Bytes 81˜96 in each row are assigned to the second channel . . . . The rest may be deduced by analogy until all the data in each row included in the frame are assigned.
3. The process for splitting OTU2 signals received during the 4n+3th (n=0, 1, 2 . . . ) frame period is described below.
Bytes 1˜16 in each row are assigned to the third channel. Bytes 17˜32 in each row are assigned to the fourth channel. Bytes 33˜48 in each row are assigned to the first channel. Bytes 49˜64 in each row are assigned to the second channel. Bytes 65˜80 in each row are assigned to the first channel. Bytes 81˜96 in each row are assigned to the second channel . . . . The rest may be deduced by analogy until all the data in each row included in the frame are assigned.
4. The process for splitting OTU2 signals received during the 4n+4th (n=0, 1, 2 . . . ) frame period is described below.
Bytes 1˜16 in each row are assigned to the fourth channel. Bytes 17˜32 in each row are assigned to the first channel. Bytes 33˜48 in each row are assigned to the second channel. Bytes 49˜64 in each row are assigned to the third channel. Bytes 65˜80 in each row are assigned to the first channel. Bytes 81˜96 in each row are assigned to the second channel . . . . The rest may be deduced by analogy until all the data in each row included in the frame are assigned.
At the receiving side, if the signals are received during the 4n+1th (n=0, 1, 2) frame period, sink frame alignment is performed on the signals in each channel based on the bytes 1-16 in the first channel. Then, signals in each channel are combined corresponding to the process for splitting OTU2 signals at the transmitting side.
If the signals are received during the 4n+2th (n=0, 1, 2) frame period, sink frame alignment is performed on the signals in each channel based on the bytes 1-16 in the second channel. Then, signals in each channel are combined corresponding to the process for splitting OTU2 signals at the transmitting side.
If the signals are received during the 4n+3th (n=0, 1, 2) frame period, sink frame alignment is performed on the signals in each channel based on the bytes 1-16 in the third channel. Then, signals in each channel are combined corresponding to the process for splitting OTU2 signals at the transmitting side.
If the signal is received during the 4n+4th (n=0, 1, 2) frame period, sink frame alignment is performed on the signals in each channel based on the bytes 1-16 in the fourth channel. Then, signals in each channel are combined corresponding to the process for splitting OTU2 signals at the transmitting side.
As can be seen from the above description that, the existing asynchronous space division dispatching method requires that the blocks of bytes of each OTUk (k=2, 3) signal frames divided in an integer-splitting way according to the total number of channels. That is, assume that the size of a frame is F bytes, the number of channels is C, the number of blocks of bytes is B, the size of each block of bytes is S bytes, then F=C×B×S. In the case where the size of a block of bytes is 16 bytes, since the OUT2 frame needs to be divided into 4 channels of 2.5 Gbps and the size of its block structure is 16320 bytes, then 16320=16 bytes/block×4 channels×255, i.e., the number of blocks of bytes assigned to each channel as a result of splitting an OTU2 frame is 255. Since the OUT3 frame needs to be divided into 16 channels of 2.5 Gbps and the size of its block structure is 16320 bytes, then 16320=16 bytes/block×16 channels×63.75, i.e., the number of blocks of bytes assigned to each channel as a result of splitting an OTU3 frame is 63.75 which is not an integer. Hence, the existing asynchronous space division dispatching cannot manage the OTU3 signals.